Accelerated smooth muscle cell (SMC) growth is known to play an important role in wound healing and in cardiovascular disease. Thus, it is important to define the factors that regulate vascular SMC growth. Whereas the differentiated state of the SMC probably has an important influence on its growth, and there is clear evidence that SMCs in atherosclerotic lesions are phenotypically altered, little is known regarding the factors that influence the differentiated state of SMCs or the possible changes in growth responsiveness that accompany differentiation and maturation. The overall objectives of this proposal are to characterize the relationship between growth and differentiation in SMCs and to determine factors that control SMC differentiation. The underlying hypothesis is that an important component of growth control in smooth muscle (SM) relates to proliferation suppressor mechanisms associated with cellular differentiation and maturation. We have previously developed quantitative biochemical and immunological markers for the SM specific isoactins and myosin heavy chains for studying SMC differentiation, as well as techniques for culturing rats aortic SMCs whereby cells can be induced to express these proteins when appropriately stimulated. The proposed studies include: 1) development to differentiation and maturation specific cDNA probes for studying SMC differentiation at the mRNA level; 2) characterization of the relationship between growth and differentiation in SM by studying the effects of growth state on SM specific protein and mRNA levels, and changes in growth responsiveness that accompany SMC differentiation; 3) identification of factors that promote SMC differentiation and maturation (assessed by expression of SM specific contractile proteins and contractile function (agonist-induced myosin light chain phosphorylation, Ca+2 transients, and cell contraction)); 4) examination of developmental changes in differentiation specific proteins and mRNAs in vivo in the rat aorta; and 5) characterization of the differentiated properties of SMCs that give rise to intimal lesions in an experimental model of atherosclerosis. Studies will provide important new insight into the role of SMC differentiation in growth control in this cell. In addition, by defining some of the parameters that stabilize the differentiated state of SMCs in culture, studies will also contribute to the development of more reliable in vitro models for studying the cellular and molecular aspects of atherosclerosis, hypertension, excitation-contraction coupling, and development of the vascular system.